Depth of field – why do you often use f/8 or more in a studio?

Why do we end up shooting at f/8, f/11 or more in the studio workshops?

- Studio workshop participant

Often the key driver of the aperture is the power from the studio lights. Whilst some lights have power settings that can be adjusted over a wide range – 5 or more stops – some only have full, half and quarter power settings or 2-stops. As the studio lights are generally more powerful than  the camera speedlites then at full power you might need to close the aperture down a lot. Also studio lights need power to illuminate some of the larger light modifiers sufficiently. Big softboxes need a lot of power to make them bright.

A side benefit of being pushed down the f/8 or more path is that the depth of field increases and this is helpful since the subjects are often people. People and their heads aren’t flat, there is often 25cm/10in or more from the back of the head to the tip of the nose. Working in relatively close to subjects with long lenses for more flattering perspective means depth of field is getting quite thin. An 85mm lens at f/8 used on a camera with an APS-C sized sensor, and focussed on a subjects eye 3 metres away gives a total depth of field of 37cm. But if focus is on the eye, then the depth that is acceptable sharp behind the eye is 20cm and in front of the eye is 17cm – it’s possible the back of the head is out of focus.

The two points above work hand in hand, and so often in the studio it’s common to use apertures of f/8 or more. Another benefit is that most lenses deliver great optical performance when stopped down to f/8.

Reference & further reading:

Online Depth of Field Calculator

Depth of field in macro photography – dpreview.com